Technical Field
The present invention relates to a gas flow monitoring method and a gas flow monitoring apparatus for monitoring a flow rate of a flow control device (a mass flow controller and others) to be used in a gas supply system for supplying gas, such as process gas, in a semiconductor manufacturing apparatus.
Related Art
In coating devices, dry etching devices, and others in a semiconductor manufacturing process, there are used for example a special gas such as silane, a corrosive gas such as chlorine gas, a flammable gas such as hydrogen gas or phosphine. The flow rate of each gas directly affects the quality of products to be manufactured in the semiconductor manufacturing process (hereinafter, also simply referred to as a “process”). Therefore, the flow rate has to be strictly controlled. In particular, in association with recent stacking and miniaturizing of semiconductor substrates, a demand for improved reliability in a process gas supply system has been increased than ever before.
For the semiconductor manufacturing apparatus, for example, a gas flow monitoring apparatus is placed in a process gas line. This process gas line includes a plurality of gas lines. These gas lines are arranged to supply process gas from a process gas supply source to a predetermined process chamber via a first line shut-off valve, a mass flow controller (hereinafter, also referred to as “MFC”, which is one example of a flow control device), and a second line shut-off valve. Since a flow rate controlled by the MFC exerts an influence on the process, a gas flow monitoring apparatus is disposed downstream of the MFC in each gas line.
FIG. 10 is a gas circuit diagram of a gas line 110 including a conventional gas flow monitoring apparatus 120. FIG. 11 is a pressure diagram in a gas flow test. As shown in FIG. 10, the gas flow monitoring apparatus 120 is provided with a start shut-off valve 21 for shutting off a flow passage for start of flow measurement, a measurement tank 22, a pressure gauge 23, and a temperature gauge 24. When a flow rate is to be measured, the gas flow monitoring apparatus 120 closes the start shut-off valve 21 to stop supply of process gas. At that time, a first line shut-off valve 12 and a second line shut-off valve 13 are open, and a MFC 10 receives a signal representing a set flow rate from the semiconductor manufacturing apparatus. In this case, as shown in FIG. 11, the process gas flowing from the start shut-off valve 21 to the MFC (one example of a flow control device) 10 is subjected to flow control by the MFC 10 and then flows to a predetermined process chamber 140. Thus, the pressure on an upstream side of the MFC 10 decreases. Therefore, a measurement time Δt required from the time when the pressure gauge 23 measures a measurement start pressure P1 to the time when the pressure gauge 23 measures a measurement end pressure P2, and a flow rate of process gas actually controlled by the MFC 10 is calculated by use of a pressure difference ΔP between the measurement start pressure P1 and the measurement end pressure P2, the measurement time Δt, and a temperature T measured by the temperature gauge 24. A signal representing the calculated flow rate is transmitted from the gas flow monitoring apparatus 120 to a semiconductor manufacturing apparatus not shown.
In the gas flow monitoring method using the gas flow monitoring apparatus 120, for example, the start shut-off valve 21 is repeatedly opened and closed at predetermined time intervals as shown in FIG. 12. In this case, supply pressure of process gas repeatedly rises and drops. The flow measurement is performed every time when the supply pressure of process gas drops. Each measured result is transmitted from the gas flow monitoring apparatus 120 to a semiconductor manufacturing apparatus not shown. Then, the semiconductor manufacturing apparatus not shown checks the MFC 10 based on a difference between the calculated flow rate and the set flow rate of the MFC 10. Accordingly, the unillustrated semiconductor manufacturing apparatus can maintain a gas flow in a gas supply system and simultaneously constantly monitor the accuracy of flow rate of the MFC 10 by use of the gas flow monitoring apparatus 120 (for example, see Patent Document 1).